TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4563
SUBJECT: GRB 060121: I-band Limits
DATE:    06/01/22 17:23:55 GMT
FROM:    Melissa Nysewander at UNC,Chapel Hill  <mnysewan@physics.unc.edu>

M. Nysewander, J. Kirschbrown, D. Reichart, P. Holvorcem, M. Schwartz
report on behalf of the UNC GRB Team:

We began imaging the error circle of GRB 060121 (Arimoto et al., GCN 4550)
at 03:58:17 UT, 5.6 hours after the burst, with the Tenagra II 32-inch
Telescope in the I filter.  The images are calibrated to 5 transformed
I-band magnitudes derived from the photometry of the SDSS (Cool et al., GCN
4554).

In a stack of 12 x 300s exposures, we do not see the optical afterglow
(Malesani et al., GCN 4561; Levan et al., GCN 4562) down to a 3-sigma
limiting magnitude of I = 20.9 at a mean time of 6.1 hours after the burst.